The invention relates to extracting oil from tailings or cuttings, for example, of the type removed from the earth during an oil drilling operation.
The waste or refuse product pulled from the earth during an oil drilling process is generally known as an xe2x80x9coil tailingxe2x80x9d or xe2x80x9coil cutting.xe2x80x9d An oil tailing typically consists of a wet, muddy, and relatively dense, sludge-like mixture of sand, dirt, oil and water. Such oil tailings can be distinguished from oil emulsions, which consist a suspension of liquid within a liquid, here of a mixture of oil and water.
In a typical oil drilling operation, hundreds of tons of oil tailings are produced. In the production of oil from subsurface bodies, the drilling requirements require safe, environmentally responsible and cost-effective oil bore mud cuttings or tailings dispersal methods. The maximum amount of oil allowed by regulatory agencies to be discharged into the ocean for off shore drilling platforms is typically about 10 Kg per 1000 Kg of tailings. Furthermore, hauling tailings ashore can be very difficult, risky and expensive. Although on-site disposal eliminates the transport risks and reduces platform storage requirements, on-site disposal requires that the tailings be disposed of at the same rate that they are generated.
The tailings processing requirements depends on the rate at which the tailings are generated from a typical well. 17.5 inch (444-mm) diameter and smaller holes are typically used to drill through oil-based mud; thus, processing requirements are usually based on a 17.5 inch hole. The volume of tailings generated in a 17.5-inch hole in 77 hours of drilling time is 1705 barrels. It is difficult to store a significant portion of this volume for later processing. As a result, the entire tailings stream must be processed as it is generated. A minimum tailings processing rate would be 14.3 tons/hour for a penetration rate of 30.5 meters per hour. Ultimately, the selected tailings cleaning rate determines the maximum sustained penetration rate which is allowed.
Due to the limited amount of storage possible on an offshore drilling platform, if the tailings processing equipment fails, drilling must stop. Moreover, because space is often limited on an oil platform and drilling rig, tailings processing equipment is preferably designed to use a minimum of space. The equipment should also be skid mounted and reasonably portable.
The invention features a system and method for separating oil from oil tailings including water.
In a first aspect of the invention, the system includes a chamber for receiving the oil tailings and an RF heating system having radiating structure for applying RF energy to heat the oil tailings to a temperature sufficient to convert the water to steam and to separate the oil from the tailings.
In another aspect of the invention, a method of separating oil from oil tailings including water, the method includes applying RF energy to the oil tailings at a temperature sufficient to convert the water to steam and to separate the oil from the tailing.
Embodiments of these aspects of the invention may include one or more of the following features.
The radiating structure is configured to have a first system voltage standing wave ratio (VSWR) characteristic (e.g., less than 2.5:1) during a first heating stage and a second VSWR characteristic during a second heating stage (e.g., greater than 2.5:1), the first VSWR characteristic being lower than the second VSWR characteristic. In a preferred embodiment, the first heating stage precedes the second heating stage. Thus, the radiating structure is configured (e.g., by tuning) to have a better impedance match during the first heating stage than the second heating stage. The lower first VSWR characteristic is used during the first heating stage when it is more desirable to have efficient energy transfer into the tailing, while the second VSWR characteristic is used where the tailing has reached a sufficient temperature that a less than optimum VSWR is acceptable for further heating of the oil.
The first heating stage is defined by the oil tailing having a temperature in a range between 95xc2x0 and 105xc2x0 C. and the second heating stage is defined by the oil tailing having a temperature greater than 105xc2x0 C. The system includes a third heating stage, preceding the second heating stage, which is defined by the oil tailing having a temperature less than 100xc2x0 C.
In certain embodiments, the system includes an air blower configured to provide air flow through the chamber, and a heat exchange system for heating the air flow provided by the air blower. Airflow is provided to the oil tailings to move heated air within the chamber, thereby providing more uniform heating of the oil tailing. The airflow is continuously provided through the chamber to keep the heat of the oil tailings below the latent heat of vaporization of water.
The radiating structure includes a slotted transmission line and, in some embodiments, includes tuning structure for adjusting the impedance of the slotted transmission line. In an alternative embodiment, the radiating structure is a capacitive structure. The radiating capacitive structure is formed by electrically isolated portions of the chamber (formed of electrically conductive walls). For example, the chamber can be formed by a pair of opposing arcuate members which together form a cylindrically shaped chamber. Alternatively, the radiating capacitive structure can include a first element formed by an integral electrically conductive outer cylindrical wall of the chamber. The second element of the radiating structure is provided by a coaxially disposed conductor, which can be an auger screw for moving the cuttings through the chamber. The system further includes a conveyor for moving (e.g., using an auger) the oil tailing from a first end of the chamber to a second end of the chamber.
In certain embodiments, the system and method further includes second radiating structure for applying RF energy to heat the oil tailing to a temperature sufficient to convert the water to steam and to separate the oil from the tailing. The second radiating structure has a third VSWR characteristic during the first heating stage and a fourth VSWR characteristic during the second heating stage. The first and fourth VSWR characteristics are smaller than the second and third VSWR characteristics.
In certain embodiments, the system and method further includes a reservoir including a fluid for increasing the viscosity of the tailings prior to introduction to the chamber; and a pump for introducing the fluid to the tailings. The fluid can include a RF absorptive material, such as carbon.
The system and method removes water from the tailings to allow the oil remaining in the tailings to be more selectively absorptive. Among other advantages, the system and method produces tailings that are substantially devoid of oil, thereby allowing the tailing to be disposed in an environmentally safe manner. The system and method are particularly advantageous for offshore drilling operations where storage and subsequent hauling of the oil tailings ashore for processing and disposal is expensive. By providing the system and method described above at an offshore site, the tailings can be processed as they are generated and then discharged back into the ocean with only the extracted oil stored for further processing. Thus, providing the system and method at an offshore operation eliminates transport risks, reduces storage requirements, and provides an environmentally safe approach for disposing of the tailings. Furthermore, the oil extracted from the tailing significantly supplements the oil recovered from the normal drilling operation. The system and method accomplishes these advantages through selective energy absorption, while operating the systems at low energy levels, thereby realizing a significant energy saving.
Other features and advantages will be readily apparent from the following description, the accompanying drawings and the claims.